It is well known for lubricant compositions to contain, in addition to a base oil, a number of additives (including friction modifiers, antiwear agents, antioxidants, dispersants, and detergents) that are used to protect internal combustion engines from wear, oxidation, soot deposits, acid build up, and the like. A friction modifier can be any material that can alter the coefficient of friction of the lubricant composition that contains it. Friction modifiers, also known as friction reducers, that change the coefficient of friction of lubricant base oils and fully formulated lubricant compositions, conventionally may include metal-containing compounds as well as ashless compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metal-ligand complexes where the metals may include alkali, alkaline earth, or transition group metals. Transition metals include Mo, Sb, Sn, Fe, Cu, Zn, Ti, and others. For example, molybdenum dithiocarbamates dithiophosphates, amines, alcohol-amides, and the like have been used. Ashless friction modifiers include lubricant materials that contain effective amounts of polar groups, for example hydroxyl-containing hydrocarbyl base oils, glycerides, partial glycerides, glyceride derivatives, and the like. Other friction modifiers include salts (both ash-containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hydroxyl-containing carboxylates, and comparable synthetic long-chain hydrocarbyl acids, alcohols, amides, esters, hydroxy carboxylates, and the like. In some instances fatty organic acids, fatty amines, and sulfurized fatty acids may be used as suitable friction modifiers.
Engine lubricant compositions containing phosphorus compounds and sulfur have been shown to contribute to particulate emissions and emissions of other pollutants. In addition, sulfur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of such catalysts.
It would be desirable to provide a lubricant composition which provides low-friction sliding between components to improve abrasion resistance in an automotive engine and vehicle fuel efficiency without compromising durability (i.e. the ability to resist wear).